Many elements, such as doors of washing machines or doors of motor vehicle glove compartments, have their opening controlled, for example by springs.
The displacement caused by the spring is generally sharply stopped by a stop. From this results more or less loud noise and violent shocks between the corresponding element and the stop.
Through French patent application 92-03741 is known a rotation-retarder by means of which the displacements of the elements, caused by the spring, are braked. This retarder includes a stator formed of two parts in the form of cups one of which fits over the other in order to form a housing in which an O-ring of elastic plastics material is arranged against the peripheral wall, while it surrounds a circular element of smaller diameter forming part of the rotor. Balls are arranged between the ring and the circular element which has notches in its periphery for this purpose. The rotary mounting of the rotor is effected by means of a small shaft which the stator includes at the centre of the housing, projecting from the bottom of the latter, the rotor piece of which the circular element forms part having in its centre a bore engaged on this shaft. This piece also includes opposite this bore a shaft which passes through the stator cover by means of a hole formed in the centre of the cover. The rotor also includes, outside the housing, a gear wheel fixed on this shaft in order to receive the rotary motion to be retarded.
With the rotation-retarder thus formed, when the rotor is rotated, the balls retained in the notches and kept in contact with the O-ring are thrust into this ring in order to brake the rotation of the rotor by the friction of contact between the balls and the O-ring.